Dynamic ram-and semiconductor device

ABSTRACT

There are provided a plurality of memory mats, including a plurality of bit lines, a plurality of word lines, and a plurality of memory cells coupled to the plurality of bit lines, and the plurality of word lines are provided in a direction of the bit line. A sense amplifier array including a plurality of latch circuits is provided in areas between the memory mats arranged in the bit line direction, respectively, and a pair of input/output nodes of which are connected to a pair of bit lines separately placed in the memory mats on both sides of the area, respectively. In this case, for a general memory mat other than both end portions in the bit line direction, word lines in any one of the memory mats are activated, while, for end memory mats provided on both end portions in the bit line direction, word lines of both memory mats are activated together.

This is a continuation of application Ser. No 10/084,514 filed Feb. 28,2002(now U.S. Pat. No. 6,545,897,) which is a continuation ofapplication Ser. No. 09/805,167, filed Mar. 14, 2001 (now U.S. Pat. No.6,373,776) which is a divisional of application Ser. No. 09/705,837,filed Nov. 6, 2000 (now U.S. Pat. No. 6,370,054), the entire disclosuresof which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to a dynamic random access memory (RAM) and asemiconductor device and more particularly, the invention relates to aneffective technique using a so-called one cross point method where adynamic memory cell is arranged at a cross point of a word line and abit line.

According to a search conducted after this invention was made, somepublications which might be related to the technology of the presentinvention, to be described later as an open bit line type (or one crosspoint method) dynamic RAM, were found, including Japanese PatentLaid-Open No. 206991/1988 (related art 1, hereinafter), Japanese PatentLaid-Open No. 13290/1989 (related art 2, hereinafter), U.S. Pat. No.5,608,668 (related art 3, hereinafter), and Japanese Patent Laid-OpenNo. 41081/1993 (related art 4, hereinafter). According to related arts 1and 2, one sense amplifier is fitted into a pitch for two bit lines bypositioning sense amplifies alternately, based on the open bit linemethod (one-cross point method). According to related arts 3 and 4,there is provided a circuit achieving, based on an electrical modelwhich is substantially the same as a bit line, for achieving a referencevoltage required for an operation by a sense amplifier provided at anend portion in a case where sense amplifiers are positioned alternatelyfor more efficient use of a chip area, as in the related arts 1 and 2.

SUMMARY OF THE INVENTION

Due to process variations, which will increase with an increase inmicronization of elements, operational conditions are expected to differlargely between a sense-amplifier at the end portion and a senseamplifier to which bit lines are equipped on both sides. Thus, accordingto reviews by the inventor hereof, it was found that the need foroperational stability will become more and more important. In therelated arts 1 and 2, no considerations are made for the arrangement atthe end portion in a case where sense amplifiers were arrangedalternately with respect to the bit lines.

Further, a cost reduction has been desired for the dynamic RAM (DRAM,hereinafter). In order to achieve such a cost reduction, reducing thechip sizes may be the most effective answer. The size of a memory cellhas been reduced by promoting its micronization. However, it will benecessary to further reduce the cell size by changing the operatingmethod of memory arrays from now on. By changing the memory arrayoperating method from the two cross point method to the one cross pointmethod, the cell size can be reduced 75% ideally based on the samedesign rule. In order to achieve a cell size reduction more effectively,the inventor hereof considered effective uses of memory cells providedat the end portion and the reduction of their area of occupation whenthe sense amplifiers are arranged alternately in the memory arrayaccording to the one cross point method as described above.

It is an object of the present invention to provide a DRAM and asemiconductor device based on the one cross point method which canachieve an improvement of operational margins and a reduction of thechip area. The above and other objects and new features of the presentinvention will be apparent from the description in this specificationand the accompanying drawings.

An outline of a typical aspect of the present invention disclosed hereinmay be described in brief as follows. There is provided a plurality ofmemory mats, including a plurality of bit lines, a plurality of wordlines, and a plurality of memory cells coupled to the plurality of bitlines and the plurality of word lines, the plurality of memory matsbeing placed in the direction of a bit line, and a sense amplifier arrayincluding a plurality of latch circuits are provided in areas betweenthe memory mats placed in the bit line direction, respectively, a pairof input/output nodes of which are connected to half of the bit linesprovided in the memory mats. In this case, for a general memory mat,other than both end portions in the bit line direction, the word linesin any one of the memory mats are activated, while, for end memory matsprovided on both end portions in the bit line direction, the word linesof both memory mats are activated together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic layout diagram showing one embodiment of a DRAM towhich the present invention is applied;

FIGS. 2A and 2B are diagrams schematically showing one embodiment of thememory mats of the DRAM according to the present invention;

FIG. 3A diagrams schematically shows one embodiment of a memory cellarray in the DRAM according to the present invention, and FIG. 3B is asection view taken along line A-A′ in FIG. 3A;

FIGS. 4A, 4B and 4C are diagrams schematically showing one embodiment ofa word system control operation of the DRAM according to the presentinvention;

FIGS; 5A and 5B are schematic circuit diagrams showing one embodiment ofa main word driver, MWD, of the DRAM according to the present invention;

FIGS. 6A, 6B and 6C are diagrams schematically showing anotherembodiment of the word system control operation of the DRAM according tothe present invention;

FIG. 7 is a schematic circuit diagram showing one embodiment of a senseamplifier portion of the DRAM according to the present invention;

FIGS. 8A and 8B are schematic circuit diagrams showing one embodiment ofa row system selector circuit of the DRAM according to the presentinvention;

FIGS. 9A and 9B are waveform diagrams showing operations of the rowsystem selector circuit of FIGS. 8A and 8B;

FIG. 10 is a block diagram showing one embodiment of an I/O circuit ofthe DRAM according to the present invention;

FIG. 11 A and 11B are schematic circuit diagrams showing one embodimentof an I/O circuit of the DRAM according to the present invention;

FIG. 12 is a block diagram showing another embodiment of an I/O circuitof the DRAM according to the present invention;

FIGS. 13A and 13B are schematic diagrams showing one embodiment of a bitline configuration on end mats in the DRAM according to the presentinvention;

FIG. 14A is an equivalent diagram of FIG. 13B, and FIGS. 14B and 14C arewaveform diagrams showing a read-out and select operation of a foldedtype end mat of FIG. 14A;

FIG. 15 is a schematic circuit diagram showing one embodiment of a senseamplifier control circuit in the DRAM according to the presentinvention;

FIGS. 16A and 16B are diagrams showing one embodiment of the folded typeend mat in the D according to the present invention;

FIGS. 17A and 17B are cross section views showing one embodiment of thefolded type end mat as seen along lines. 1-1′ and 2-2′ of FIGS. 16A and16B, respectively;

FIG. 18 is a schematic diagram showing another embodiment of a bit lineconfiguration of the end mat in the DRAM according to the presentinvention;

FIG. 19 is a schematic diagram showing another embodiment of the bitline configuration of the end mat in the DRAM according to the presentinvention;

FIG. 20 is a schematic layout diagram showing one embodiment of the DRAMto which the present invention is applied;

FIG. 21 is a magnified view of end mats and general mats adjacentthereto in a memory bank BANK 1 shown in FIG. 20;

FIG. 22 is a schematic circuit diagram showing one embodiment of an FXdriver and a sub-word driver according to the present invention;

FIG. 23 is a layout diagram showing one embodiment of the FX driver andthe sub-word-driver according to the present invention;

FIG. 24 is a schematic flayout diagram showing another embodiment of theDRAM according to the present invention; and

FIG. 25 is an overall block diagram showing one embodiment of the DRAMaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic layout diagram of one embodiment of a dynamic RAM,DRAM, to which the present invention is applied. In FIG. 1, a main partis emphasized among individual circuits constituting the DRAM to whichthe present invention is applied, and it is formed over onesemiconductor substrate of single crystal silicon based on knowntechnology for manufacturing a semiconductor integrated circuit, forexample.

In this embodiment, a memory array can be divided into, but not limitedto, four parts as a whole. They can be separated to the left and theright with respect to the longitudinal direction of a semiconductorchip. Provided on a center part 14 are an address input circuit, aninput/output interface circuit having a data input/output circuit and abonding pad array and power supply circuits including step-up andstep-down circuits. A memory array control circuit (AC) 11 and a mainword driver (MWD) 12 are positioned in a part contact with the memoryarrays on both sides of the center part 14. The memory array controlcircuit 11 has a control circuit and a main amplifier for driving asub-word select line and/or a sense amplifier. A column decoder area(YDC) 13 is provided at a vertical center part about the longitudinaldirection in each memory array divided into four, that is, two above andtwo below or two on the left and two on the right, with respect to thelongitudinal direction of the semiconductor chip, as described above.

In each of the memory arrays, the main word driver 12 forms selectsignals for a main word line which extends through one correspondingmemory array. A driver for a sub-word select line for sub-word selectionis provided in the main word driver area 12 and generates a selectsignal for the sub-word select line which extends in parallel with themain word line, as will be described later. The column decoder 13generates a select signal for a column select line which extends throughone corresponding memory array.

Each of the memory arrays is divided into a plurality of memory cellarrays (memory mats, hereinafter) 15. As shown in its magnified view,the memory mat 15 is formed so as to be surrounded by sense amplifierareas 16 and sub-word driver areas 17. A part where the sense amplifierarea 16 and the sub-word driver area 17 cross is called a cross area 18.A sense amplifier provided in the sense amplifier area 16 is constitutedby a latch circuit in the CMOS configuration and is of a so-called onecross point method or open bit line type, which amplifies signals ofcomplementary bit lines extended to the right and the left with respect,to the sense amplifier. The sense amplifiers are positioned alternatelywith respect to the bit lines. Thus, the bit line provided in the memorymat is divided in half and allocated alternately to two sense amplifierarrays sandwiching them.

One memory mat 15 shown in the magnified view includes 512 sub-wordlines (word lines) and 1024 data lines, that is one of the complementarybit lines orthogonal to them. In one of the memory arrays, 32 memorymats 15 are provided as regular mats and two memory mats 15 are providedas redundant mats in the direction the bit lines extend. Since theredundancy memory mats, or end memory mats, have half of the memorycells, as will be described later, two end memory mats are needed to beequivalent to one. The end memory mats may be used for reference. Inthis case, one memory mat is allocated for redundancy.

Since the memory mat 15 is provided with a pair of complementary bitlines with the sense amplifier 16 as its center, the bit lines aredivided essentially into 16 by the memory mats 15 in the bit lineextending direction. Further, four of the memory mats 15 are provided inthe word line extending direction. Thus, in the word line extendingdirection, the sub-word line is divided into four by the memory mats 15.

In one memory mat 15, there are provided 1024 bit lines, except for theend memory mats, and, therefore, memory cells equal to about 4K areconnected thereto in the word line direction. Further, there areprovided 512 sub-word lines, and, therefore, memory cells equal to512×32=16 K are connected thereto in the bit line direction.Accordingly, one memory array has a memory capacity that amounts to4K×16k=64M bits, and so four memory arrays have a memory capacity thatamounts to 4×64M=256M bits.

It should be understood that the term “MOS” herein originally and simplyrefers to a metal oxide semiconductor configuration. However, thesedays, the term MOS generally includes a device in which the metal ofessential parts of a semiconductor device is replaced by a non-metalelectrical conductor, such as poly-silicon, or where an oxide isreplaced by another insulator. Also, the term CMOS. is understood ashaving a wide technical meaning depending on the variation of what MOSrefers to, as described above. The term MOSFET is also understood ashaving a wide meaning. Virtually, the term MOSFET has recently becomeunderstood as including a configuration in a broad sense, which can beconsidered as an insulating gate field effect transistor. The terms CMOSand MOSFET herein are based on those general meanings.

FIGS. 2A and 2B show diagrams of one embodiment of memory mats of adynamic RAM, DRAM, according to the present invention. FIG. 2A showscircuits corresponding to two memory mats MAT0 and MAT1 equipped in ahierarchical word line method DRAM as shown in FIG. 1. FIG. 2B shows alayout corresponding to them. In FIG. 2A, a memory cell MC including aMOSFET and a cell storage CS is connected to each of all cross points ofa bit line BL and a sub-word line WL. A sense amplifier SA is connectedto the bit line BL, while a sub-word driver SWD is connected to the wordline WL.

In this embodiment, in order to reduce t e number of main word lines, orin other words, in order to moderate the wiring pitch of the main wordline, four sub-word lines in the direction of the complementary bitline, but not limited thereto, are positioned for one main word line, aswill be described later. A sub-word select driver is positioned in thedirection of the main word line in order to select one sub-word lineamong those sub-word lines, which are divided in two in the main wordline direction, as shown in FIG. 1, and four of which are al locatedtoward the complementary bit line direction, respectively. The sub-wordselect driver forms a select signal for selecting one from four sub-wordselect lines which extend toward the direction of the sub-word driverarrangement (sub-word driver array SWDA). The main word line MWL isextended in parallel with the sub-word line WL, not shown. The columnselect line YS is positioned in parallel with the bit line BL extendeddirection orthogonal thereto, not shown.

Sense amplifiers SA in a sense amplifier array SAA provided between thetwo memory mats, MAT0 and MAT1, are connected to the complementary bitlines extending to both sides of the two memory mats, MAT0 and MAT1. Onesense amplifier SA of these sense amplifiers SA is positioned for, butnot limited to, each two bit lines in the sense amplifier array SAA.Therefore, in case there are 1024 bit lines BL as indicated above, 512(half of 1024) sense amplifiers SA are provided in the sense amplifierarray SAA provided between the memory mats MAT0 and MAT1.

In the memory mat MAT0, the remaining 512 bit lines are connected to thesense amplifiers SA provided in the sense amplifier array SAA, which isthe opposite side of the memory mat MAT1. In the memory mat MAT1, theremaining 512 bit lines are connected to the sense amplifiers SAprovided in the sense amplifier array SAA provided in the opposite sideof the memory mat MAT0. When sense amplifiers SA are distributed on bothsides in the bit line direction, one sense amplifier may be formed forevery two bit lines separately and alternately on both ends thereof.Thus, the sense amplifier SA and the bit line BL can be matched in pitchin order to form memory mats and sense amplifier arrays with higherdensity.

This is the same in the sub-word driver SWD. 512 sub-word lines WLprovided in the memory mat MAT0 are divided into 256 each and connectedto the 256 sub-word drivers SWD in the sub-word driver array SWDApositioned on both sides of the memory mat MAT. In this embodiment, twosub-word lines WL are used as one pair and every two sub-word driversSWD are distributed. In other words, the sub-word lines corresponding totwo memory cells, which have a common connection portion to the bitlines, are used as one set and two sub-word drivers are positioned atone end of the memory mat MAT0 (upper side of FIG. 2A). Two sub-wordlines similar to the above and adjacent to them are also used as one setand positioned at the other end of the memory mat MAT0 (lower side ofFIG. 2A).

The sub-word driver SWD, not shown, generates a select signal for thesub-word line of the memory mats provided on both sides sandwiching thesub-word driver array SWDA in which the sub-word driver SWD is formed.Thus, the sub-word driver SWD may be distributed efficiently based onthe sub-word line formed in accordance with the memory cell arrangementpitch. Further, the sub-word line WL can be selected faster.

A memory cell MC is formed at each cross point of a bit line BL and asub-word line WL in the memory cell arrays (or memory mats) MAT0 andMAT1 surrounded by the sub-word driver array SWDA and the senseamplifier array SAAL for example. In the memory mat MAT0 in which eachof the memory cells MC is formed, as shown in FIG. 2B, an upperelectrode (plate electrode) PL in the storage capacitor CS is a flatelectrode formed commonly in all of the memory cells MC within thememory mats MAT0 and MAT1. The plate electrode PL is fed at the borderof the sub-word driver array SWDA and memory mats MAT0, MAT1 from apower supply wiring VPLT wired in the bit line BL extending directionthrough the connection point PLCT. In FIG. 2A, the storage node SN is abottom electrode of the storage capacitor CS and the connection pointwith an address select MOSFET is shown.

In this embodiment, as shown in FIG. 2B, the plate electrodes PL0 andPL1 as above formed in the memory mats MAT0, MAT1, respectively, whichexist on both sides of the sense amplifier array SAA are connected toeach other through a wire PLSA using the plate layer itself. Further, aplurality of wires PLSA are provided through the sense amplifier arraySAA in order to reduce the resistance between the two plate electrodesPL0 and PL1 significantly. Thus, when micro-signals read out from thememory cell MC selected between the complementary bit lines BL of thememory mats MAT0 and MAT1 are amplified by the sense amplifier SA,noises which have opposite phases relative to each other generated inthe plate electrodes PL0 and PL1 can be canceled rapidly, which allowsfor a significant reduction of the noises caused in the plate electrodesPL0 and PL1.

FIGS. 3A and 3B show illustrative diagrams of one embodiment of a memorycell array in a DRAM according to the present invention. FIG. 3A shows alayout of memory cell arrays in two memory mats MAT0 and MAT1. FIG. 3Bshows an element cross section taken on line A-A′ in FIG. 3A. In FIG.3A, layout and cross section of a sense amplifier SA area providedbetween the MAT0 and MAT1 are omitted.

The memory cell array includes active regions ACT of the MOSFET, aconnection point (contact)-SNCT for connecting between a storage node SNof the memory cell and a source/drain diffusion layer corresponding tothe storage node SN of the MOSFET formed in the active region ACT, and aconnection point (contact) BLCT for connecting between a bit line BL anda source/drain diffusion region corresponding to an input/outputterminal of the memory cell corresponding to the bit line BL of theMOSFET formed: in the active region ACT. The structure shown in FIG. 3Bfurther includes a capacitance insulating layer of a memory capacitor.Here, a first mdtal layer Ml and a bit line BL are in the same wiringlayer and a first poly-silicon layer FG and a sub-word line WL are onanother wiring layer.

As shown in FIG. 3B, the plate electrode PL of the memory mats MAT0 andMAT1 provided on both sides of the sense amplifier SA does not terminateon the sense amplifier SA, but is connected through an electrode itselfconstituting the plate electrode PL. Thus, the resistance between theplate electrode PL of the memory mat MAT0 and the plate electrode. PL ofthe memory mat MAT1 can be reduced significantly. The COB (Capacitorover Bitline) structure is used for the memory cell. That is, a storagenode SN is provided on the bit line BL. Thus, the plate electrode PL isnot divided in the memory mat MAT by the bit line BL and the connectionpoint BLCT of the address select MOSFET, and one flat plane can beformed. Therefore, the resistance between the plate electrodes can bereduced.

In this embodiment, as shown in FIG. 3B, the plate electrode PL isadvantageously a stacked layer structure, such as the PL (D) and PL (U),which can reduce the sheet resistance value of the plate electrode PL.As one example, when a high dielectric layer, such as BST and Ta2O5, isused for the capacitance insulating layer CP of the storage capacitor,the capacitance of the storage capacitor CS can be increased by using Rufor the bottom electrode (storage-node) SN and the upper electrode lowerlayer PL (D). Since. Ru has a lower sheet resistance value than that ofpoly-Si, which has been used conventionally, the resistant value of theplate electrode PL can be reduced.

When W is stacked as the plate electrode PL (U) in the structure, theresistance value of the plate electrode PL can be further reduced. Thus,when the resistant value of the plate electrode PL itself is reduced,the noises on the plate electrode PL can be cancelled faster and theplate electrode PL noises can be reduced. TiN can be used for the plateelectrode PL (D), also. In such a case, the same result as thatdescribed above can be obtained.

The memory cell structure described above includes a connection pointSNCT for connecting the storage node SN and a source/drain diffusionlayer of the MOSFET, which is adjacent to the bit line BL, as shown inFIG. 3A. In other words, a signal path is provided for transmitting achange in potential of the bit line BL to the storage node when aparasite capacitance exists between the storage node of the memory celland the bit line BL in the vertical direction of the cross section.Thus, it is advantageous to connect the plate electrodes PL mutually bywiring using itself.

FIGS. 4A, 4B and 4C are diagrams for illustrating one embodiment of acontrol operation of the word system in the DRAM according to thepresent invention. For the structure of the memory mat, as shown in FIG.4(A), four memory mats arranged in the bit line direction arerepresented for illustrative purposes. Memory mats on both sides in thebit line direction are called end memory mats (simply called an end mathereinafter), while a memory mat sandwiched by sense amplifiers SA iscalled a general memory mat (simply called a general mat hereinafter).Since the sense amplifiers SA are connected to the bit line for everyother memory mat, half of the bit lines are regarded as a dummy in theend mats. Thus, when word lines in the end mat are selected, the numberof memory cells to be selected will be half of the number of word linesin the general mat if selected.

A word line is selected by the sub-word driver SWD distributed at thetop and the bottom of the memory mat. The sub-word driver SWD respondsto a select signal for the main word lines formed in the main worddriver MWD provided in common for memory mats aligned in the word lineextending direction, not shown, and a sub-word line select signal toselect one sub-word line (sometimes simply called a word linehereinafter) from the four sub-word lines allocated to one main wordline.

In this embodiment, the sense amplifiers are distributed on both sidesof the bit line in the memory mat. When a plurality of memory mats areprovided in the bit line direction, a pair of end mats is provided atboth end portions. Thus, in order to use end mats only half of whosememory cell can be selected irregularly, as described above, effectivelyas a data storage area equal to the general mat, word lines on both sideend pats are concurrently selected.

As shown in FIGS. 4B and 4C for the illustrative purposes, when each offour bit lines exists on the general mats 0 and 1, two sense amplifiersSA provided in the sense amplifier block (SA block) 0 are connected totwo bit lines BLB of the end mat and two bit lines BLT of general mat 0.Two sense amplifiers SA provided in the sense amplifier block 1 areconnected to two bit lines BLB of the general mat 0 and two bit linesBLT of general mat 1. Then, two sense amplifiers SA provided in thesense amplifier block 2 are connected to two bit lines BLB of thegeneral mat 1 and two bit lines BLT of an end mat. In the end mat, bitlines, which are not connected to the sense amplifier, are regarded as adummy.

For example, when word lines of the general mat 0 are selected, the wordlines can select four memory cells crossing four bit lines. Storedinformation in the four memory cells are amplified by the senseamplifiers of two sense amplifier blocks 0 and 1 provided across thegeneral mat 0. Then, a rewriting (refresh) operation is performed wherea memory charge being almost lost by a storage capacitor due to the wordline selection operation is recovered to the original charge condition.In other words, the dynamic memory cell performs a destructive read-outoperation by turning ON the address select MOSFET through the word lineselection operation, connecting the storage capacitor to the bit lines,and causing a charge share with the bit line parasitic capacitance tocause in the bit lies changes in micro-voltage in accordance with thememory charge. Thus, the dynamic memory cell requires a rewritingoperation for the memory cell selected during amplification by the senseamplifier connected to the bit line crossing word lines to be selected.

On the other hand, when word lines on the end mats are selected, onlytwo memory cells can be selected because the word lines on the end matare constituted by crossing two bit lines and two dummy wires.Therefore, when data is written in or read out by selecting the wordlines of the end mat also, only half of the data can be input or output,which deteriorates its effectiveness as a memory. Accordingly, as shownin FIG. 4C, when the word lines of the end mat are selected, word linesof the end mats on both sides are always selected. Thus, the number ofmemory cells to be selected by one word line selection can be four,which is equal to the number when a general mat is selected. In thisway, according to the easy configuration where two word lines are alwaysselected concurrently for the end mats, data can be written and read outby the same bit line selection operation in the same manner as thegeneral mat.

According to this configuration, the end mats can be used effectively asa part of the memory area. Thus, in the micronized memory cell, forexample, a read-out margin of the sense amplifier can be allocated, and,further, the chip occupying area per bit can be smaller as compared withthe case where bit lines in the enct mat are used only for forming areference voltage for the reading-out operation by the sense amplifierin order to allocate a read-out margin for the sense amplifier.

FIGS. 5A and 5B are circuit diagrams of one embodiment of the main worddriver MWD of the DRAM according to the present invention. FIG. 5A showsa main word driver in the general mat, while FIG. 5B is a main worddriver corresponding to two end mats. In FIG. 5A, a signal RMST<15:0> isa mat select signal when 32 memory mats are divided into 16 in sets oftwo as shown in FIG. 1. Signals RF3T and RF6T are predecode signals. Inthe general mat, pre-charge MOSFET Q3 in the selected mat is turned offby the pre-charge signal RMSXDPT<15:0>. At the low level of the signalRMST<15:0>, in one memory mat array (four memory mats in the exampleshown in FIG. 1), through MOSFETs Q1 and Q2 turned ON by the predecodesignals RF3T and RF6T, the pre-charge voltage of an input terminal of aninverter circuit IV 1 is discharged. With the low level of the inputterminal, the select signal RMWLB of the main word line becomes lowlevel of the select level.

Unselected word lines in the selected mat maintains a pre-charge voltagecorresponding to the unselected level since the low level correspondingto the pre-charge voltage of the input signal of the inverter circuit IVI turns on a P channel type feedback MOSFET Q4 provided between theinput terminal and operational power supply terminal. In the unselectedmemory mat, the pre-charge signal RMSXDPT<15:0>remains at the unselectedlevel of the low level, which maintains the pre-charge operation.

In FIG. SB, a signal RMSET is a select signal for the end mat, andsignals RF3T and RF6T are predecode signals. In the end mats, apre-charge MOSFET in the end mat is turned off by the pre-charge signalRMSXDPET corresponding thereto. At the low level of the signal RMSET, ina two-end-mats array (four memory mats in the example shown in FIG. 1),through MOSFET turned ON by the predecode signals RF3T and RF6T, thepre-charge voltage of an input terminal of each inverter circuit IV 1 isdischarged. With the low level of the input terminal, the select signalRMWLB of the main word line corresponding to the two end mats becomeslow level of the select level.

Unselected word lines in the selected mat maintain a pre-charge voltagecorresponding to the unselected level since the low level correspondingto the pre-charge voltage of the input signal of the inverter circuitturns on a P channel type feedback MOSFET provided between the inputterminal and the operational power supply terminal, in the same manneras the case of the general mat. When the word line of the general mat isselected, the pre-charge signal RMSXDPET remains at the unselected levelof the low level, which maintains the pre-charge operation in the endmat.

According to the hierarchical word line method, the sub-word line (wordline) on the lower layer is selected by the selection operation of themain word line. Thus, the main word driver of the end mat can be causedto perform word line selection for the end mat by means of each circuitchange, which may generate a concurrent selection condition.

FIGS. 6A, 6B and 6C are diagrams of another embodiment of a controloperation for the word system of the DRAM according to the presentinvention. The memory mat configuration, as shown in FIG. 6A, representsseven memory mats arranged in the bit line direction for illustrativepurposes. Memory mats on both ends in the bit line direction areregarded as end mats. Among the general mats which are sandwiched bysense amplifiers SA, one placed at the center is called a center mat andis handled essentially as an end mat. This configuration is suitable fora case where two general mats are selected concurrently. In other words,it is suitable for the case where 32 memory mats are divided into twosets of 16 as shown in FIG. 1 in order to address the word systemselection control when two memory mats are selected concurrently.

When word lines of the general mats 0 and 2 are selected concurrently asshown in FIG. 6B so as to increase the read/write bit numbers, two wordlines of the end mats and a word line of the center mat are combined asshown in FIG. 6C. In other words, a memory cell connected to the senseamplifier (sense amplifier block) 2 on the left side of the center matis combined with a memory cell connected to the left side end mat and abit line. A memory cell of a bit line connected to a sense amplifier(sense amplifier block) 3 on the right side of the center mat iscombined with a memory cell connected to the right side end mat and thebit line.

For example, when two sets of mat configurations shown in FIG. 4A areprovided, the read/write bit numbers can be increased in the same manneras indicated above. However, the arrangement would have four end matsand then four word lines to be activated, which increases the currentconsumed by the word line selection. Further, in the end mat, the numberof dummy bits is increased, which increases the occupied area per bit.In the configuration where a center mat is placed as indicated above andhalf of the bit lines are combined with the bit lines of end mats onboth sides, the generation of the number of the dummy bit can beminimized, which reduces the occupied area and the select circuit forthe bit lines can be common.

In this case, the center mat it is not necessary to locate at the centerof the memory mat array. In FIG. 6A, a general mat 0 adjacent to theleft side end mat can be used as the center mat. However, in such acase, the distances between the center mat (general mat 0) and the leftend mat and the right end mat differ significantly. Thus, a transmissionpath for writing-in or reading-out signals is ruled by a slower one,which slows the operational speed substantially. Therefore, as in theembodiment shown in FIG. 6A, a general mat physically provided at thecenter of an array including a plurality of memory mats is preferablyused as the center mat.

FIG. 7 is a circuit diagram of one embodiment of a sense amplifierportion of a dynamic RAM according to the present invention. The senseamplifier SA is constituted by a CMOS latch circuit including N-channeltype amplified MOSFETs QS and Q6 and P channel type amplified MOSFETs Q7and Q8, which are in a latch form where a gate and a drain arecross-connected. The sources of the N-channel type MOSFETs QS and Q6 areconnected to common source line SDN. The sources of P-channel typeMOSFETs Q7 and Q8 are connected to a common source line SDP. Groundvoltage VSS and operational voltage VDL of the circuit are supplied tothe common source lines SDN and SDP through a power switch MOSFET, notshown. The power switch MOSFET may be, but not limited to, provided bybeing distributed in the sense amplifier portion.

A pre-charge (equalize) circuit including an equalize MOSFET Q11 forshorting the complementary bit lines BLTO and BLBO and switch MOSFETs Q9and Q10 for supplying a half pre-charge voltage VDL/2 to thecomplementary bit lines BLTO and BLBO is provided in the input/outputnode of the sense amplifier SA. Commonly supplied to the gates of theseMOSFETs Q9 to Q11 are pre-charge (bit line equalize) signals BLEQ. Adriver circuit for forming the pre-charge signals BLEQ, not shown,includes an inverter circuit provided in the cross area 18 shown in FIG.1 so as to make its starting-up faster. In other words, prior to theword line selection timing at the beginning of a memory access, theMOSFETs Q9 to Q11 forming the pre-charge circuit are caused to switchfaster through the inverter circuit distributed in each of the crossareas 18.

A pair of input/output nodes of the sense amplifier SA are connected tothe complementary bit lines BLTO and BLBO as well as to local (sub)input/out put lines LIOT and LIOB extended along the sense amplifierarray via a column (Y) switch circuit including MOSFETs Q12 and Q13. Thegates of the MOSFETs Q12 and Q13 are connected to the column select lineYS, and they are turned ON when the column select line YS is at theselect level (high level), which connects the input/output node of thesense amplifier SA to the local input/output lines LIOT and LIOB.Similar sense amplifiers, pre-charge circuits and column switch circuitsare provided for other complementary bit lines BLT1, BLB1, BLT2, BLB2,also.

Thus, the input/output node of the sense amplifier SA amplifies a minutevoltage change for the bit line half pre-charge voltage, which changesin accordance with a memory charge of a memory cell connected to a crosspoint with a word line of a selected memory mat between two memory mats(the MAT0 and MAT1, for example) provided across the input/output noie,by using a half pre-charge voltage of a bit line on an unselected memorymat side. The selection by the column select line YS is transmitted tothe local input/output lines LIOT and LIOB through the column switchcircuits (Q12 and Q13).

As shown in FIG. 1, the local input/output lines LIOT and LIOB areextended over a sense amplifier array aligned in the main word lineextending direction. Further, a sub-amplifier circuit is provided in thelocal input/output lines as necessary to transmit amplifier signals.Then, as will be described later, it is connected to a main input/outputline MIO aligned in the bit line direction and guided to a data outputcircuit or a data input circuit.

FIGS. 8A and 8B are circuit diagrams of one embodiment of a row systemselector circuit for the DRAM according to the present invention. Thisembodiment describes a partial circuit of the row system selectorcircuit where one of the end mats or general memory mats are used as aredundant circuit. FIG. 8A shows as a reference example a row systemselector circuit in accordance with a folded bit line method and sharedsense amplifier method. FIG. 8B shows a circuit diagram of a pre-chargecontrol signal generator circuit and main word driven in accordance withthe redundancy memory mats.

According to the shared sense amplifier method, when one of memory matsprovided on both sides of the sense amplifier is used, a mat selectsignal RF9T, after a relief determination that a failed word line or bitline exists on the normal memory mat side, generates a shared'switchcontrol signal SHR and a pre-charge signal BLEQ corresponding to theredundant memory mat. Then, the switch control for the shared switchMOSET and termination of the pre-charge circuit are matched in time by adelay circuit (delay), and a main-word line-corresponding to theredundant memory mat is selected.

On the other hand, when the end mat or the center mat of this embodimentis used as a redundant circuit, a timing signal RACT of a general matcorresponding to a regular circuit generates a pre-charge control signalconcurrently with the regular circuit. Then, the main word line for theredundant mat uses the mat select signal RF9T of the relief determinedredundant mat to select the main word line of the redundant mat. In thisconfiguration, since the pre-charge operation needed for causing themain word line to be available for selection has already been carriedout in advance, the main word line can be selected without inserting adelay circuit (delay), as described above.

According to the configuration, when there is no failure in the regularcircuit, the word line of the redundant mat is not selected. Thus, thereis no problem if the pre-charge operation is terminated. Since thepre-charge circuit performs the pre-charge operation in response to thetermination of the regular circuit operation, any problem will occur inthe selection operation of the redundant circuit in the next memorycycle even when the pre-charge voltage of the bit line is reduced insome degree due to a leakage current, for example.

FIGS. 9A and 9B show waveform diagrams for illustrating operations ofthe row system selector circuit shown in FIGS. 8A and 8B. FIG. 9Acorresponds to the circuit operation of the row system selector circuitin the FIG. 8A as a reference while FIG. 9B corresponds to the circuitoperation of the now system selector circuit in FIG. 8B according to thepresent invention.

As shown in FIG. 9A, in the configuration where the shared switch selectsignal SHR and the pre-charge signal BLEQ are turned to the low levelafter the redundancy determination (hit) of the redundant mat, thetiming for selecting the word line SWL has to be delayed by providing adelay circuit as described above in order to allocate a time needed forthose operations. Here, in the regular mat, the signals SHR, BLEQ andFXB remain at the high level and the sub-word line SWL is also in theunselected state since the mat itself is unselected based on theredundancy determination (hit).

On the other hand, according to the present invention, as shown in FIG.9B, the pre-charge signal BLEQ and the sub-word select line FXB of theredundant mat are tuned to the low level in response to a clock signalCLK without waiting for the redundant determination (hit) of theredundant mat. Then, the redundancy determination (hit) turns thesub-word line SWL to the select state. The sub-word select line FXB willbe described later. In the regular mat, the pre-charge signal BLEQ andthe sub-word select line FXB are turned to the low level in response tothe clock signal CLK. Then, the redundancy determination (hit) returnsthe pre-charge BLEQ and the sub-word select line FXB to the high level.

FIG. 10 is a block diagram of one embodiment of an I/O (input/outputline) circuit of DRAM according to the present invention. In thisembodiment, memory mats include end mats and two general mats in thesame manner as FIG. 4. Local input/output lines LIO<0>, LIO<L> andLIO<2> are provided to the sense amplifier blocks (SA blocks) 0, 1 and2, respectively, formed by being sandwiched between each of memory mats.

On the other hand, main input/output lines MIO<O> and MIO<L> areprovided in the memory mat array direction, that is, in the bit lineextending direction. Thus, when data is exchanged in 2 bits in thememory mat configuration, the local input/output lines LIO<0> and LIO<L>are associated with the main input/output lines MIO<0> and MIO<I>,respectively. Then, when a word line of the general mat 1 as describedin note (a) is selected, the remaining local input/output line LIO<2>has to be associated with the main input/output line MIO<0> so as toavoid a data collision, since the local input/output line LIO<L> isassociated with the main input/output line MIO<I>.

However, in the end mat as described above, in a case where two wordlines arc selected concurrently, the local input/output line LIO<2>corresponding to the right side end mat has to be associated with themain input/output line MIO<1> so as to avoid a data collision since thelocal input/output- line LIO<0> corresponding to the left side end matis associated with the main input/output line MIO<O>, which is oppositeto the case where the word line of the general mat 1 is selected.

Accordingly, in this embodiment, a selector switch is provided betweenthe main input/output lines MIO<0> and MIO<1> for the local input/outputline LIO<2> provided in the sense amplifier block 2 provided between oneend mat and a general mat as described above. Thus, the signaltransmission path is switched over in order to achieve the associationas described above in accessing the general mat and in accessing an endmat.

FIGS. 11A and 11B show circuit diagrams of one embodiment of aninput/output circuit (I/O circuit) of the DRAM according to the presentinvention. FIGS. 11A and 11B are the circuit diagrams of the LIO-MIOswitching circuit in the embodiment shown in FIG. 10. In thisembodiment, a CMOS bus gate type switch is shown. Similar results can beobtained in case of connection by the sub-amplifier, for example.

In the same manner as the line LIO<0> in FIG. 10, the local input/outputline LIO and the main input/output line MIO are connected selectively inone-to-one relationship. When the memory mat is unselected, a pre-chargesignal BLEQ corresponding thereto is turned to the high level. Then, thecomplementary local input/output lines LIOT0 and LIOB0 are maintained inthe pre-charge voltage VBLR state by an equalize MOSFET and a pre-chargeMOSFET in order to turn off the CMOS switch MOSFETs Q20 to Q23.

When the memory mat is selected, the pre-charge signal BLEQcorresponding thereto is turned to the low level, which turns off theequalize MOSFET and the pre-charge MOSFET of the complementary localinput/output lines LIOT0 and LIOB0. Then, CMOS switch MOSFETs Q20 to Q23are turned on, which connects the local input/output lines LIOT0 andLIOB0 to the main input/output lines MIOT0 and MIOB0. In thisconfiguration, the same operation is performed in the switch circuitbetween the local input/output line LIO<1> and the main input/outputline MIO<1>.

In order to switch over between the main input/output lines MIO<0> andMIO<1> depending on the mat selection state in the same manner as theline LIO<2> in4FIG. 10, MOSFETs Q20 to Q23 and Q24 to Q27, for formingCMOS switch circuits, are provided, respectively. Then, when a generalmat is selected, the signal MSB is turned to the low level, which turnson the switch MOSFETs Q20 to Q23 and connects the complementaryinput/output lines LIOT2 and LIOB2 to the main input/output lines MIOT0and MIOB0, as described above. When an end mat is selected, the signalMSEB is turned to the low level, which turns on the switch MOSFETs Q24to Q27 and connects the complementary input/output lines LIOT2 and LIOB2to the main input/output lines MIOT1 and MIOB2, as described above.

In this case, a switch is provided between the local input/output lineLIO and the main input/output line MIO. A plurality of localinput/output lines LIO are allocated to the main input/output line MIO,and only a selected one is connected to the main input/output line MIO.That is it has been described for the case where it is applied tohierarchical input/output lines. However, the same selector switch isprovided for the local input/output line corresponding to one end mat asdescribed above even when the local input/output line LIO and the maininput/output line MIO are directly connected.

FIG. 12 is a block diagram of another embodiment of an input/output line(I/O) circuit of the DRAM according to the present invention. In thisembodiment, in the same manner as FIG. 6A, memory mats include two endmats, a center mat and general mats. Sense amplifier blocks (SA blocks)0 through 5 formed by being sandwiched between each of the memory matsare provided with local input/output lines LIO<0> to LIO<5>,respectively.

On the other hand, main input/output lines MIO<0> to. MIO<3> areprovided in tie memory mat array direction, that is, in the bit lineextending direction. Thus, when memory mats are divided into two setsand data is exchanged in 2 bits from each set, that is four 4 bits as awhole in the memory mat configuration, the local input/output linesLIO<1> and LIO<2> are associated with the main input/output lines MIO<1>and MIO<0>, respectively, in one set, while in the other set, the localinput/output lines LIO<3> and LIO<4> are associated with the maininput/output lines MIO<2> and MIO<4>, respectively.

In this case, when a word line of the general mats 0 and 3 is selectedas shown in FIG. 11(A), local input/output lines LIO<0> and LI0<5> haveto be associated with the main input/output lines MIO<0> and MIO<2>,respectively, so as to avoid data collision, since the localinput/output lines LIO<1> and LIO<4> are associated with the maininput/output lines MIO<1> and MIO<3>, respectively.

On the other hand, when word lines of two end mats and a center mat areselected as shown in FIG. 11(B), local input/output lines LIO<0> andLIO<5> have to be associated with the main input/output lines MIO<1> andMIO<3>, respectively, so as to avoid data collision, since the localinput/output lines LIO<2> and LIO<3> are associated with the maininput/output lines MIO<0> and MIO<2>, respectively.

Accordingly, in this embodiment, a selector switch is provided betweenthe main input/output lines MIO<O> and MIO<1> and MIO<2> and MIO<3> forthe local input/output lines LIO<0> and LIO<5> provided in the senseamplifier blocks 0 and 5 provided between one end mat and a general matas described above. Thus, the signal transmission path is switched overin order to achieve the association as described above in accessing thegeneral mat and in accessing an end mat.

FIGS. 13A and 13B are schematic diagrams of one embodiment of a bit lineconfiguration in an end mat of the DRAM according to the presentinvention. FIG. 13A is a diagram illustrating the array configurationwhere a sense amplifier is arranged alternatively at one simple crosspoint. In the end mat, an invalid bit line exists as it is withoutconnection to the sense amplifier SA. The same end mat is provided onthe other side of the sense amplifier SA corresponding to a memory matMATn, but it is omitted here. Since an invalid bit line (dummy bit line)as described above exists, the number of valid memory cells provided inthe end mat would be half of those in the general mat. Thus, word linesin the end mats on both sides are selected concurrently. That is, thecombination of two end mats produces a memory access equivalent to thatwith one general mat.

FIG. 13B shows a folded bit line in the end mat. In other words, awiring area for the invalid bit line is utilized for the location of thefolded bit line of the end mat. Folding the bit line reduces the lengthof the end mat in the bit line direction to the half of the length ofthe general mat in the bit line direction, which achieves an areareduction of the end mat. This area reduction is achieved in the othermemory mat, resulting in an area reduction equal to one general mat.

When a plurality (N) of memory mats exist in the word line direction,areas equal to N general mats can be reduced as a whole. It should benoted that in the dynamic RAM as described for the embodiment in FIG. 1,there are four memory arrays as a whole and an area equal to fourgeneral mats can be reduced in each memory array. Thus, area reductionequal to 16 general mats can be attempted in the whole chip.

FIGS. 14B and 14C are waveform diagrams for a reading out selectionoperation for the folded type end mat. When the bit line is folded forarea reduction of the end mat, as shown in FIG. 14A, read-out chargesfrom two memory cells are transmitted to the bit line by the word lineselection operation. In other words, the read-out signal amount of thebit line of the end mat as shown in FIG. 14C is twice as much as theread-out amount of the bit line of the general mat as shown in FIG. 14B.

Accordingly, the overdrive period of a sense amplifier for amplifyingreadout signals of the bit line of the end mat is made shorter than theoverdrive period defined in the sense amplifier when the micro-signalsof the bit line of the general mat are amplified. Alternatively, whenthe readout signals of the bit line of the end mat are amplified, theoverdrive of the sense amplifier is omitted. This timing adjustmentallows readout operations which are almost equivalent between those withthe end mat and the general mat.

FIG. 15 is a circuit diagram of one embodiment of the sense amplifiercontrol circuit. When a word line of an end mat is selected, two senseamplifier arrays operate with a relatively large distance. Then, theconvergence of current required for the amplifying operation by thesense amplifier is reduced in the wire for supplying an operationalvoltage. As a result, efficient current supply is achieved. In otherwords, since the voltage decrease gets smaller in the power supply linedue to the increase in the operational current, the amplifying operationby the sense amplifier can become faster by as much.

In addition, when a bit line is folded in the end mat as described aboveand two memory cells are selected by selecting one word line, the signalamount read out id the bit line as described above would be twice.Accordingly, two start-up signals are provided for reducing the senseamplifier over driver period when the end mat is selected. The signalRSAET is a sense amplifier start-up signal. When the end mat isunselected, the high level of the signal MSWEB generates overdrivepulses during the period equal to the delay time produced by thetransmission of a delay signal through two delay circuits (delay) Then,this turns on the MOSFET Q30 so that the over drive pulses such as powersupply voltage VDD are supplied to a common source line SDP of theP-channel type MOSFET of the sense amplifier.

On the other hand, when the end mat is selected, the signal MSEB isturned to the low level. This opens the gate for transmitting a delayoutput from one delay circuit. Thus, over drive pulses are generatedduring the period equal to the delay time, which turns on the MOSFETQ30. Thus, this can prevent the sense amplifier from being over drivenexcessively when the end mat is selected. After the delay timecorresponding to the over drive has passed, the MOSFET Q30 is turned offand MOSFET Q31 is turned on so that the operational voltage inherent tothe sense amplifier such as VDL is supplied. In the common source lineSDN of the N-channel type MOSFETs, the high level state of the start-upsignal RSAET turns on OSFET Q32 so that ground potential VSS of thecircuit is transmitted.

In the DRAM of this embodiment, the power supply voltage VDD is arelatively high voltage such as 3.3 V or 2.5 V. It is stepped down bythe VDL to a lower voltage such as 2.2 V or 1.8 V. When the senseamplifier starts its amplifying operation, a higher overdrive voltagesuch as VDD is used as the VDL so that the start-up to the VDL in thebit line gets faster in order to cause either one of the complementarybit lines BLT and BLB to be at the high level in accordance with thestored information in the memory cell. When the signal amount is largeras in the end mat and the overdrive period is longer, a problem that thehigh level of the bit line exceeds VDL occurs. Thus, the timingadjustment as described above is necessary.

FIGS. 16A and 16B are schematic layout diagrams of one embodiment of thefolded type end mat. In FIG. 16A, a bit line connected to oneinput/output node of a sense amplifier SA on one end is folded at themiddle in its extending direction. In other words, a bit line and aninvalid bit line adjacent thereto are connected and folded at the middleportion and the remaining half is omitted. In this embodiment, inconsideration of the layout of the sense amplifiers, two neighboring twobit lines, but not limited thereto, are validated, and the invalid bitlines are positioned on both sides. The portion of the invalid bit linesis used to allow the upper bit line to be folded to the upper side andthe lower bit line to be folded to the lower side. The repetition ofthis pattern constitutes the end mat.

As shown in FIG. 17A, the connection of the folded part is achieved byusing a first polysilicon layer FG constituting a gate electrode and aword line of the MOSFET in the folded portion and an FG contact, but theinvention is not limited thereto. As shown in the cross section in 3,the bit lines are regarded as a first metal layer Ml. The FG contactconnects FG and Ml. When the phase shift method, which is one ofmicromachining technologies, is used, the adjacent bit lines are formedin a different process. Thus, they have to be connected to each other byFG and a FG contact as described above.

In FIG. 16B, one end of a bit line connected to one input/output node ofthe sense amplifier SA is folded by using every other bit line at themiddle portion in its extending direction. In other words, the bit lineconnected to one sense amplifier branches off at the connection portionwith the sense amplifier so as to produce every other bit and extends upto a length equal to half of the general mat bit line. The bit lineconnected to the sense amplifier and the adjacent sense amplifierextends up to a length equal to the half of the general mat bit lengthwithout branching off from the connection portion. Then, it is foldedand further extends toward the sense amplifier between the branched offbit line. In other words, the branched off bit line and the folded bitline are positioned alternately. The repetition of the pattern describedabove constitutes the end mat.

The connection of the folded portion is as shown in FIG. 17B, and thebit line is constituted by a first metal layer Ml as shown in the crosssection in 3, but is not limited thereto. In other words, when the phaseshift method, which is one of the micromachining technologies asdescribed above, is used, every other one of the bit lines are formed.Thus, the branched off bit line and the folded bit line can be formedintegrally in respective processes.

FIG. 18 is a schematic diagram of another embodiment of the end mat bitline configuration in the DRAM according to the present invention. Inthis embodiment, it is assumed that the end mat includes a folded bitline. Thus, two memory cells are connected in parallel at a cross pointof a word line and a bit line. This end mat is, but not limited to, aredundant mat for relieving a failed word line in the general mat.

When the end mat is used as a redundant mat as described above, thenumber of memory cells to be connected to the word line is reduced tohalf. Thus, the word line is selected in both end mats in the samemanner as indicated above. The configuration where the end mat is usedas a redundant mat and two memory cells are positioned at a cross pointof the word line and the bit line as described above not only reducesthe area occupied by the end mat, but also it produces excellent effectsincluding an increase in the relief efficiency.

Connecting two memory cells to the bit line in parallel can double thesignal amount as described above. In other words, in the end mat, almostnone of the memory cells cause a failure due to a short informationholding time. Thus, this can significantly reduce the probability forcausing a failure that the information holding time is short in theredundant mat when switched to the redundant mat, which results in arelief failure.

FIG. 19 is a schematic diagram of another embodiment of the end mat bitline configuration in the DRAM according to the present invention. Inthis embodiment, the end mat includes a folded bit line, which is usedfor reference of the general mat. In this case, the word line is fixedto a circuit ground potential VSS or bit line half pre-charge voltageVDL/2. Fixing the potential of the word line can reduce noises caused inthe end mat when reading out.

FIG. 20 is a schematic layout diagram of one embodiment of a DRAM towhich the present invention is applied. In this embodiment, a memoryarray is divided into four in the same manner as that in FIG. 1, andthey form memory BANK0 to BANK3, respectively. As represented by onememory bank BANK1, for the illustrative purposes, 33 memory mats and twoend mats are provided in the bit line direction (YS) and four memorymats are positioned in the word line direction (MWL).

Provided in the longitudinal center part of a semiconductor chip are aninput/output interface circuit including a data input/output circuit anda bonding pad array and a power supply circuit including a step-upcircuit and/or a step-down circuit. A main word driver MWD is positionedalong the center part and drives a main word line MWL positioned suchthat it can reach each sub-word driver through the four memory mats. Acolumn decoder area YDC is provided in the lateral end part of thesemiconductor chip and drives a column select line YS, which extendstherefrom through the 33 general mats and one end mat to the senseamplifier array corresponding to them.

In this embodiment, a center mat provided at the center of the 33general mats arranged in the bit line direction and the end mat are usedas redundancy mats MAT. In other words, the memory mats shown in FIG. 6Aor 12 are divided into two sets in the center part and one word line isselected in general mats in each set. When a word line failure occurs inthe general mat selected in either one of the sets, two word lines ofthe center mat and the end mat are selected for word line failurerelief. When the bit line of the end mat is folded as described above sothat two memory cells form a redundancy cell, two word lines may beselected at the same time in the center mat.

FIG. 21 shows a magnified view of the end mats and general mats in thememory bank BANK1 shown in FIG. 20. In this embodiment, the hierarchicalword line method is adopted, and a word line provided in a emory mat isselected based on a combination of a main word line MWL and a sub-wordselect signal FX. The sub-word select signal FX is an operationalvoltage of the sub-word driver SWD, as will be described later, and itsvoltage level is a select signal of the sub-word line.

In the dypamic memory cell, information charges are supplied to astorage capacitor through an address select MOSFET. In order tocommunicate the high level of the bit line to the storage capacitor, thegate voltage of the MOSFET has to be equal to or higher than a thresholdvoltage of the MOSFET for the high level of the bit line. The effectivethreshold voltage of the address select MOSFET is raised by forming agate insulating film so as to be thicker or by supplying a negativeback-bias voltage to the substrate in order to reduce leakage current inthe off state (sub-threshold leakage current).

Therefore, the select level of the sub-word line has to be the step-upvoltage VPP, which is higher than the threshold voltage of the MOSFETwith respect to the high level of the bit line (VDL or VDD). Thus, an FXdriver is needed for communicating a sub-word line select, signalcorresponding to the step-up voltage to each sub-word driver SWD. The FXdriver corresponding to the sub-word driver SWD of the general mat maybe provided in a cross area where a sense amplifier array SA and asub-word driver array SWD intersect. On the other hand, when the crossarea does not exist because the memory bank end terminates at a memorycell in the alternate sense amplifier positioning in the open bitconfiguration, the FX driver cannot be provided.

When the end mat is used only for reference, the word line may be at thefixed level as described above. Thus, the sub-word driver is notnecessary and the problem described above is not caused. On the otherhand, when it is used as a redundant mat as in this embodiment, thesub-word driver has to be operated for failed word line relief. In thisembodiment, a part of the redundant array SWD is used as an FX driverarea in the end mat. In other words, when the end mat is used as aredundant mat, all of word lines formed therein do not have to beutilized. Thus, the end portion word line is used as a dummy word lineand the sub-word driver area corresponding to it us used as the FXdriver area.

In this embodiment, four sub-word lines WLO to WL3 are provided with,onemain word line MWL, and sub-word select lines FX0 to FX3, FX0B to FX3Bare needed or selecting one of the four sub-word lines. In thismbodiment, sub-word lines provided in one memory mat are selected halfand half by sub-word driver arrays SWDA provided on both sides of thememory mat. In other words, in the memory mat as shown in FIG. 2,sub-word drivers are distributed to both sides of the memory mat forevery two word lines in order to achieve staggered positioning in thesame manner as the sense amplifier. Therefore, when four sub-word lineare selected with one main-word line as described above, the sub-worddrivers for generating sub-word select signals for selecting onesub-word line among the four sub-word lines are provided for every othermemory mat in two groups, one for sub-word select signals FX0 and FX2and the other for sub-word select signals FX1 and FX3.

FIG. 22 is a circuit diagram of one embodiment of an FX driver and asub-word driver according to the present invention. The sub-word driverincludes a CMOS inverter circuit and an N.: channel type MOSFET providedbetween an output of the CMOS inverter circuit and a ground potential ofthe circuit. Select signals MWLB from the main word line are commonlysupplied to input terminals of two CMOS inverter circuits provided inthe sub-word driver area. The main word select signals MWLB are commonlysupplied to the CMOS inverter circuits provided in the sub-word driverregion provided in the other end of a redundancy mat in FIG. 22 in orderto select four sub-word lines.

The sub-word line select signals FX0 and FX2 formed in the FX driversare supplied to power supply terminals of the two CMOS invertercircuits, that is, source terminals of a P channel type MOSFET includedin the CMOS inverter circuits, respectively. The operational voltage ofthe FX drivers is used as a step-up voltage VPP, which is a select levelof the sub-word line select signals FX0 and FX2. The input signals FX0Band FX2B supplied to the input terminals of the FX drivers are suppliedto the gate of the N channel type MOSFET provided between the output ofthe sub-word driver and the ground potential of the circuit. The FXdriver and its adjacent FX driver form the sub-word line select signalsFX1 and FX3.

When the select signals MWLB of the main word line is at a low level,the P channel type MOSFET is turned ON and the N channel type MOSFET isturned OFF in the CMOS inverter circuit. Therefore, the sub-word lineSWL0 or SWL2 is turned to the VPP level in the sub-word driver SWD inwhich the sub-word line select signal FX0 or FX2 are turned to theselect level VPP by the FX driver. Here, sub-word line select signalFX0B or FX2B of the unselected one is turned to the high level, whichthen turns the switch MOSFET ON in order to fix the sub-word line SWL0or SWL2 at the circuit ground potential. The sub-word line SWLcorresponding to an area where the FX driver is provided is used as, butis not limited to, a dummy word line, which is also used as, but is notlimited to, an unselect level, such as the circuit ground potential.

FIG. 23 is a layout diagram of one embodiment of an FX driver and asub-word driver according to the present invention. The FX driver formsoperational voltages of a plurality of sub-word drivers so that itincludes an N channel type MOSFET (NMOS) and a P channel type MOSFET(PMOS) larger than MOSFETs included in the sub-word driver shown in FIG.23, for illustrative purposes. In order to form the FX driver with largesize MOSFETS, as described above, 36 word lines formed in an end mat areused as dummy word lines. The FX driver is formed in a sub-word driverregion corresponding thereto.

FIG. 24 is a schematic layout diagram of another embodiment of a dynamictype RAM according to the present invention. In this embodiment, amemory array is divided into, but not limited to, four as a hole. Thus,two memory arrays are provided separately in the longitudinal directionof the semiconductor chip and two memory arrays are provided separatelyin the lateral direction of the semiconductor chip. Those describedabove are the same as the embodiments of FIGS. 1 and 20.

In this embodiment, word lines are placed along the chip in thelongitudinal direction, and bit lines are placed along the chip in thelateral direction. In other words, the directions of the bit lines andword lines are opposite to those in FIGS. 1 and 20. In each memory arraydivided into four as a whole including two vertically and twohorizontally with respect to the longitudinal direction of thesemiconductor chip as described above, X-system pre-decoder and reliefcircuits and Y-system predecoder and relief circuits, for example, areplaced at the middle portion with respect to the longitudinal direction.A main word driver area MWD is formed along the middle portion of thememory array and drives main word lines which are extended toward thebottom or the top in accordance with each memory array.

In the memory array, a Y decoder Y DEC is provided on the periphery ofthe chip, which is opposite to the chip center portion. The memory arrayis divided into a plurality of memory mats as described above. Thememory mat is formed by being surrounded and sandwiched by senseamplifier areas and sub-word driver areas. The cross portion of thesense amplifier area and the sub-word driver area is called a crossarea. The sense amplifier is provided in the sense amplifier area basedon the one-cross point method and staggered positioning.

A select operation by the Y system is transmitted to the Y decoderplaced on the periphery of the chip through an address buffer providedin the center part of the chip via a relief circuit and the predecoderprovided in the middle portion of the memory array. Then, a Y selectsignal is formed in the Y decoder YDEC. A bit line of one memory matarray is selected by the Y select signal. Then, it is transmitted to amain amplifier MA provided in the chip center part on the opposite sideand is amplified and output through an output circuit provided in thechip center part.

In this configuration, it may be seen that signals are routed in thechip, so that a longer time to output a readout signal. However, anaddress signal needs to be input as it is in the relief circuit.Thus,.when the relief circuit is placed in he chip center, the outputtiming by the predecoder is determined based on the check resultsregarding whether or not it is a failed address. In other words, whenthe predecoder and the relief circuit are spaced away from each other,signal delays may cause a delay in the actual Y select operation.

In the signal transmission path for reading-out signals in the memoryarray, according to a layout scheme where the Y decoder exists at thecenter part of the chip, when performing reading-out from complementarybit lines of the memory mat on the periphery of the chip on the oppositeside, the amount of time needed for traversing the memory array in orderto transmit the Y select signal is added to the amount of time neededfor the readout signal from the complementary bit lines of the memorymat on the periphery of the chip to traverse the memory array in thedirection opposite to the direction of the Y select signal through aninput/output line, in order to be transmitted to the main amplifier areadded.

In other words, in the worst case, it takes a longer time due to theflow of a signal making one round trip to the memory array. However,according to the present invention, the main amplifier MA and the Ydecoder YDEC are placed on both sides of t he memory array. Therefore,the sum of signal transmission path times for selecting complementarybit lines of the memory mat and the signal transmission path fromselected complementary bit lines to the input of the main amplifier MAthrough the input/output line can be reduced to half of the one roundtrip path time because the signal transmission path according to thepresent invention only traverses the memory array even if eithercomplementary bit line is selected.

In the layout as described above, it is further advantageous that theend mats are aligned in the longitudinal direction of the chip close tothe center of the chip. When the sense amplifier is placed in the onecross point method and in the staggered manner, the memory array endswith the memory cell. In other words, according to the conventional twocross points method, the memory array ends with a sense amplifier. Thus,the Y select line needs to be extended to the sense amplifier. on theother hand, according to the one cross point method as described in thisembodiment, the memory array ends with memory cell. Therefore, the Yselect line can be terminated at the sense amplifier array providedbetween a general mat and an end mat.

According to this configuration, a Y select line does not exist in thearea where an end mat is formed. As a result, in the cross section inFIG. 3B, a second metal wiring layer M2 and a third metal layer M3 areused for the Y select line and the main word line. However, either oneof the second or third wire used as the Y select line on the end mat isin the idle state. Thus, the second or third wire corresponding to the Yselect line on the end mat may be used as a signal wire for peripheralcircuits provided in the center part.

With an increase in the functions of the dynamic RAM, the peripheralcircuits provided at the center of the chip needs to be configured witha random logic circuit and a more complicated signal line has to beformed, rather than a regular circuit configuration, such as a memoryarray. In other words, in the dynamic RAM, wires are extremely congestedand many signal lines are needed. Therefore, using an area on the endmat as the wiring area can virtually reduce the number of wires in thechip center area. In the mat configuration as described above, nearly100 signal lines can be formed, and nearly 200 wires are extended to theend mat array direction in the most congested area in the peripheralcircuit. Therefore, it is meaningful to use the end mat as the wiringarea.

FIG. 25 is an overall block diagram of one embodiment of the dynamic RAMaccording to the present invention. Control input signals include a rowaddress strobe signal RAS, column address strobe signal/CAS, writeenable signal/WE and output enable signal/OE, where “/” is an over-barof a logic symbol indicating the low level is at the active level. Xaddress and Y address signals are input from a common address terminalAdd in time series simultaneously with the row address strobe signal/PASand the column address strobe signal/CAS.

The X address and Y address signals input through an address buffer arecaptured by a latch circuit. The X address signal captured in the latchcircuit is supplied by a predecoder as described above. The outputsignal is supplied to an X decoder and a select signal for the word lineWL is formed. With the operation for selecting a word line, a readoutsignal as described above appears in the complementary bit lines of amemory array and a sense amplifier performs an amplifying operation. TheY address signal captured in the latch circuit is supplied to apredecoder as described above. The output signal is supplied to an Ydecoder and a select signal for the bit line DL is formed. X and Yrelief circuits store a failed address and compare the stored failedaddress and the captured address signal. If they match, the X and Yrelief circuits instruct the X or Y decoder to select a spare word lineto or bit line inhibit the selection of the regular word line or regularbit line.

The one selected by the column switch circuit, not shown, is connectedto the common input/output line and the stored information amplified bythe sense amplifier is transmitted to the main amplifier. The mainamplifier is, but not limited thereto, an amplifier, which can be alsoused as a write circuit. In other words, during the readout operation,readout signals read out through the Y switch circuit are amplified andoutput from an external terminal I/O through an output buffer. Duringthe write operation, write signals input from the external I/O arecaptured through the input buffer, and transmitted to the commoninput/output line and the select bit line through the main amplifier. Inthe select bit line, the write signal is transmitted by the amplifyingoperation by the sense amplifier, and charges corresponding to them areheld in the capacitor in the memory cell.

A clock generator circuit (main control circuit) generates each ofvarious kinds of timing signals needed for the select operation for amemory cell, such as a capture control timing signal for an addresssignal input in with the signals /RAS and /CAS and/or an operationtiming signal for the sense amplifier. An internal power supplygenerator circuit receives an operational voltage, such as Vcc and Vss,supplied from the power supply terminal and generates each of theinternal voltages, such as the plate voltage, a pre-charge voltage, suchas Vcc/2, internal step-up voltage VCH, internal step-down voltage VDL,and substrate back bias voltage VBB. A refresh counter generates anaddress signal for refreshing and is used for the selection operation ofthe X system in the refresh mode.

In this embodiment, an end mat control circuit is provided. Thus, whenit is arranged that reading-out and/or writing-in are also performed onthe end mat and when two word lines corresponding to end mats areselected, switching the main amplifier in accordance with it andswitching the IO switch circuit for avoiding data collision as describedabove are also performed. When an end mat is used as a redundancycircuit, a word line of the end mat can be selected with a signal fromthe X relief circuit. Thus,-the end mat control circuit can be replacedby that.

Operational effects, which may be obtained from the embodimentsdescribed above, are as follows:

(1) A dynamic RAM according to an aspect of the present inventionincludes a plurality of memory mats including a plurality of bit lines,a plurality of word lines, and a plurality of memory cells coupled tothe plurality of bit lines and the plurality of word lines, theplurality of memory mats being arranged in the direction of the bitline, and a sense amplifier array including a plurality of latchcircuits being provided in areas between the memory mats arranged in thebit line direction, respectively, and a pair of input/output nodes ofwhich are connected to half of the bit lines provided in the memorymats. In this case, for a general memory mat other than both endportions in the bit line direction, word lines in any one of the memorymats may be activated while, for end memory mats provided on both endportions in the bit line direction word lines of both memory mats may beactivated concurrently. Thus, an operational margin of the senseamplifier can be allocated, and, further, an area occupied per bit canbe smaller as a result of effective use of the end mats.

(2) Further, a bit line in the end memory mat may be formed by using anarea twice as long as the bit line pitch of the bit line of the generalmemory mat, and its length in the bit line extending direction may beshorter than the length of the general memory mat in the bit lineextending direction. Thus, the occupied area in the end mat can besmaller.

(3) Further, a bit line in the end memory mat may be formed by beingfolded at a distance equal to or more than half of the general memorymat from a connection portion with the latch circuit of the senseamplifier array. Thus, the occupied area in the end mat can be smaller,and, further, the amount of signals can be larger when storedinformation is read out also from the end mat.

(4) Further, the end memory mat bit line may include a combination of afirst bit line pair including two bit lines branching off at intervalstwice as long as the bit line pitch from a connection portion with thelatch circuit of the sense amplifier array and extending to a halflength of the bit line of the general memory mat, and a second bit linepair extending linearly to half the length of the bit line of thegeneral memory mat from the connection portion with the latch circuit ofthe sense amplifier array and being folded back therefrom so as to besandwiched by the first bit line pair. Thus, when wires are formed basedon the phase shift method, the first and the second bit lines can beformed integrally.

(5) Further, the gates of MOSFETs of two memory cells connected to onebit line may be connected to the word line of the end memory mat. Thus,the occupied area in the end mat can be smaller, and, further, theamount of signals can be larger when stored information is read out alsofrom the end mat.

(6) Further, the dynamic RAM may include a plurality of firstcomplementary input/output lines extended along the sense amplifierarray, and the sense amplifier array may include a pre-charge circuitfor supplying a pre-charge voltage corresponding to a middle voltage ofan operational voltage of the sense amplifier to the complementary bitline pair and a column switch MOSFET. Thus, each element needed forselecting a memory cell can be placed rationally.

(7) The dynamic RAM may further include second complementaryinput/output lines 1 and 2 in common in accordance with the plurality ofmemory mats, whereby first complementary input/output lines provided ina sense amplifier array corresponding to one end memory mat areconnected to the second complementary input/output lines, and a selectorswitch whereby, first complementary input/output lines provided in asense amplifier array corresponding to the other end memory mat areconnected to the second complementary input/output line 1 when a bitline of a general memory mat is selected, and are connected to thesecond complementary input/output line 2 when a bit line in the endmemory mat is selected. Thus, data collision can be prevented for theend mat and data can be written in or read out.

(8) Further, word lines may be divided into virtually two sets at acenter memory mat provided in a center portion among memory mats placedin the bit line extending direction, and an operation for selecting amemory cell may be performed by combination of half of the bit lines inthe center memory mat and bit lines in the end memory mat. Thus, datacan be input/output for more memory cells.

(9) Further, a timing control may be performed so that the amplificationspeed of the sense amplifier gets slower when a word line in the endmemory mat is selected. Thus, the reading out operation from the generalmat can be matched.

(10) Further, the dynamic RAM may have a hierarchical structureincluding the word line including a main word line and a sub-word linedivided into several parts in an extending direction of the main wordline, and may further include a sub-word driver in accordance with thedivided sub-word lines. Preferably, in this case. a plurality of thesub-word lines are allocated to the main word line, and the sub-worddriver receives a signal of the main word line and a signal of asub-word select line to select one sub-word line among a plurality ofthe sub-word select lines.

(11) Still further, a memory cell provided in the end memory mat may beused as a redundant memory cell used for relieving a failed memory cell.Thus, the larger signal amount can allow a higher relief efficiency forfailed word lines.

(12) Further, a preparation operation for the word line selection in arow system selector circuit provided in accordance with the end memorymat may be performed at the same timing as a preparation operation forthe word line selection in a row system selector circuit provided in ageneral memory mat. Thus, it allows faster memory access.

(13) Further, a memory cell provided in the end memory mat may be as aredundant memory cell use for relieving a failed memory cell, and adriver circuit of the sub-word select line may be formed in a part ofthe area where a sub-word driver is formed and a bit line provided in anend memory mat corresponding to a the driver circuit may be used as adummy word line. Thus, an area occupied by the selector circuit in theend mat can be smaller.

(14) A dynamic RAM according to another aspect of the present inventionincludes a plurality of memory mats including a plurality of bit lines,a plurality of word lines, and a plurality of memory cells coupled tothe plurality of bit lines and the plurality of word lines, theplurality of memory mats being arranged in the direction of the bitline, and a sense amplifier array including a plurality of latchcircuits being provided in areas between the memory mats arranged in thebit line direction, respectively, and at pair of input/output nodes ofwhich are connected to half of the bit lines provided in the memorymats. In this case, for end memory mats provided on both end portions,the bit lines may be used as a fixed voltage for keeping the MOSFET OFFfor forming a reference voltage and an area equal to two bit linepitches for the bit lines of the general memory mat may be used so thatits total length and number of memory cells to be connect ed arevirtually the sane as the bit line of the general memory mat. Thus, theoperational margin of the sense amplifier can be allocated and furtherthe occupied area can be smaller.

(15) Further, in that case, the bit lines in the end memory mat may beformed by being folded at a distance equal to half of the general memorymat from a connection portion with the latch circuit of the senseamplifier array. Thus, the operational margin of the sense amplifier canbe allocated, and, further, the occupied area can be smaller.

(16) Further, the end memory mat bit line may include a combination of afirst bit line pair branching off at intervals twice that of a bit linepitch from a connection portion with the latch circuit of the senseamplifier array and extending to a length half that of the bit line ofthe general memory mat and a second bit line pair extending linearly tothe length half that of the bit line of the general memory mat from theconnection portion with the latch circuit of the sense amplifier arrayand being folded back therefrom so as to be sandwiched by the first bitline pair. Thus, when wires are formed based on the phase shift method,the first and the second bit lines can be formed integrally.

(17) Further, in this case, a plurality of sets of the plurality ofmemory mats may be provided in the bit line direction and in the wordline direction in order to constitute one memory array. Also,preferably, at least two of the memory arrays are carried by asemiconductor chip, and a column selector circuit for forming a selectsignal of the bit line is provided adjacent to one end memory mat in amemory array corresponding to an end portion of the semiconductor chip.In addition, a wiring layer, which is the same as a wiring layer fortransmitting a selector signal of the bit line on the other end memorymat, may be used as a part of a wiring layer of a peripheral circuitprovided in a semiconductor chip center portion sandwiched by the twomemory arrays. As a result, it can ease wiring in the chip centerportion sandwiched by the two memory arrays.

While the invention made by the inventor hereof has been described basedon its preferred embodiments, it should be understood that the presentinvention is not limited to each of those embodiments, and that variouschanges and modifications may be made without departing from the spiritand scope of the invention. For example, the word line may constitute atwo layer structure along with a metal layer instead of the hierarchicalword line method. The input/output interface of the dynamic PAM may beadjusted for various devices such as DDR SDRAM and SDRAM. The dynamicRAM may be built in a digital integrated circuit. The present inventioncan be utilized widely for a dynamic RAM and a semiconductor devicewhere sense amplifiers are arranged in a staggered tanner based on theone cross point method.

Effects which can be obtained from the typical aspect of the presentinvention disclosed herein may be described in brief as follows: Thereare a plurality of memory mats including a plurality of bit lines, aplurality of word lines, and a plurality of memory cells coupled to theplurality of bit lines and the plurality of word lines, the plurality ofmemory mats being arranged in the direction of the bit line, and a senseamplifier array including a plurality of latch circuits being providedin areas between the memory mats arranged in the bit line direction,respectively, and a pair of input/output nodes of which are connected tohalf of the bit lines provided in the memory mats, wherein, for ageneral memory mat, other than both end portions in the bit linedirection, word lines in any one of the memory mats are activated while,for end memory mats provided on both end portions in the bit linedirection, the word lines of both memory mats are activatedconcurrently. Thus, the operational margin of the sense amplifier can beallocated, and, further, the occupied area per bit can be smaller as aresult of effective use of the end mats.

What is claimed:
 1. A semiconductor memory comprising: a first memoryarray having a plurality of first bit lines extending in a firstdirection, a plurality of first word lines and a plurality of firstdynamic memory cells; a second memory array having a plurality of secondbit lines extending in said first direction, a plurality of second wordlines and a plurality of second dynamic memory cells; and a plurality ofsense amplifiers formed in an area between said first memory array andsaid second memory array, wherein each of said plurality of senseamplifiers has a pair of input terminals connected to one of said firstbit lines and one of said second bit lines, wherein each length of saidsecond bit lines is shorter than each length of said first bit lines,and wherein said second memory array is used as a redundant memoryarray.
 2. A semiconductor memory according to claim 1, wherein anothersecond bit line is connected to said one of said second bit lines, andwherein two of said second dynamic memory cells are connected to one ofsaid pair of input terminals when one of said second word lines isselected.